Proteins respectively protein preparations are considered as raw materials for the food and feed industries. They find much use in industrial chemistry, for example in the production of adhesives, emulsions for photographic coats and cosmetics just to name a few applications.
The major significance of protein preparations for all living things, for products and materials of the entire food chain and for a multiplicity of products and materials for industrial applications are based on the functional properties of the individual proteins, such as being water-bound or oil-bound, foam formation, moreover dispersion, solubility, gel formation, viscosity, emulsifiability and thermostability.
Depending on the type of proteins, their functional properties are different and change essentially in dependence of certain parameters, such as for example in dependence of the ambient temperature or the pH value. Depending on the technical requirements, the functional properties of protein preparations can be selectively adjusted by selecting the external parameters, such as disclosed for example in DE 197 21 079 A1. Thus, solubility, viscosity and other certain functional properties for technical applications can be selectively adjusted by means of corresponding selective thermal treatment.
In the industrial production of protein preparations based on vegetable proteins, of the legumes lupine seeds and peanuts, peas and soybeans are of the greatest significance as a starting product compared to all the other vegetable starting materials because legumes possess approximately 40% protein. Oilseeds, for example poppy seeds, sesame seeds, coconuts, almonds, linseeds, rape seeds, sunflower seeds etc. as well as wheat, corn, rye etc., are vegetable starting products for producing protein preparations even if they contain less protein than the aforementioned legumes.
For large-scale production of protein preparations, in particular for the production of protein isolates which have a protein content of more than 90% as dry substance, legumes such as soybeans or lupines undergo multistage process steps.
First the proteins are extracted from the starting materials with the aid of an alkaline aqueous solution after, if required, the starting materials had undergone a preceding acidic extraction. The extraction, which is carried out under alkaline conditions, is followed by precipitation of the proteins under acidic conditions. Finally the proteins precipitated in this manner are dried and are then available for suited technical as well as food-related applications. A prior art method of production is, for example, disclosed in DE 198 13 207 C1.
The protein preparations produced with the prior art methods of production respectively isolation possess, due to the method of separation utilized in their production, pH-value dependent solubility properties, which have a marked minimum in particular in the case of acid pH values, i.e. in the case of pH values of <7 and in particular in the case of pH values from 4 to 5, protein preparations produced in this manner are poorly soluble in water respectively completely insoluble in water.
The protein preparations produced with prior art methods behave in the same manner with regard to their functional properties, for example with regard to emulsification and foam formation. Accordingly, the protein preparations emulsify significantly worse in an acid range than in a neutral respectively slightly alkaline range, i.e. the ability to stabilize emulsions worsens considerably. Emulsifiability plays an important role especially in the food and cosmetic industries, for example in the production of dressings, sauces, mayonnaise or cosmetic products such as creams or salves and technical products such as adhesives, glues, rubber mixtures, etc.
For many applications, however, for example in the areas of food production, cosmetics as well as in the area of technical products it is desirable to use protein products whose functional properties are largely independent of parameters such as, in particular, the pH value, ionic strength and/or temperature. Such type protein preparations cannot, however, be produced with the present methods of production, in particular, not on a large industrial scale. Production methods for protein preparations having these property profiles are based on modifying the proteins, which occurs following protein production and is usually technically very complicated, such as is carried out, for example, using hydrolytic enzymes.